PAYG phones are auto-enabled for roaming once they're used in the UK. Pay-monthly users need to enable roaming thus unlocking access to foreign networks - usually done by texting ROAMING to 150 from the UK.
You'll receive a text message on first arrival abroad, offering add-ons to reduce the cost of roaming.
Costs are at https://ee.co.uk/help/help-new/roaming-costs
